iqdb: add more info to iqdb thumbnails.

* Add the source (twitter, pixiv, etc) and upload date ("X minutes ago")
  to iqdb thumbnails.
* Link the filesize to the full file so you can compare files in new tabs.
* Link the similarity to a iqdb search so you can pivot your search to other posts.

app/presenters/post_presenter.rb

@@ -21,6 +21,7 @@ class PostPresenter < Presenter
     end
 
     locals = {}
+    locals[:post] = post
 
     locals[:article_attrs] = {
       "id" => "post_#{post.id}",
@@ -74,7 +75,7 @@ class PostPresenter < Presenter
     end
 
     if options[:similarity]
-      locals[:similarity] = options[:similarity].round
+      locals[:similarity] = options[:similarity].round(1)
     else
       locals[:similarity] = nil
     end